Can I integrate Workflow Designer into an Angular app?

Yes, you can. In fact, Workflow Engine's Designer can be integrated into any HTML page, since it runs on JavaScript. However, if you don’t want to bother integrating Designer, you can use Workflow Engine Server, which offers the following benefits:

It comes with a pre-integrated Designer;

It has a REST API, which allows you to use regular http queries to create processes, get and execute commands, etc.